A work machine such as a wheel loader has a gear shifting control device that includes a torque converter and a transmission, and transmits the motive power of an engine to wheels through the torque converter and transmission for traveling purposes. The transmission has clutches for forward traveling, reverse traveling, first gear, second gear, third gear, and fourth gear. A solenoid valve is provided for each clutch. The transmission selectively outputs an instruction current to a solenoid valve in order to supply hydraulic oil to the associated clutch and engage it.
In the gear shifting control device described above, the clutch engagement feeling does not always remain unchanged due, for instance, to the manufacturing error and assembling error involved in the transmission and solenoid valves even when the same instruction current is output to different solenoid valves for the transmission. Under such circumstances, learning control is exercised as indicated in Japanese Patent JP-A-2003-287119 to learn the clutch pressure, correct any clutch pressure error, and determine an optimum hydraulic pressure characteristic value.
Patent Document 1: JP-A-2003-287119